Low-capacity fuse construction



Feb. 13, 1934. E. v. SUNDT LO W CAPACITY FUSE CONSTRUCTION Filed Jan. 20, 1932 7 M 41 J 5 5 1 1 4m 4 2 J 1 4. g 1 w 1 5 9 1 I 1 6 5 7 l 4 4 L2 9 7 Z i Edward VSzNM/Z INVENTOR BY MA /5o,

ATTORNEYS Patented Feb. 13, 1934 UNITED STATES PATENT OFFICE 7 Claims.

My invention relates to improvements in lowcapacity fuse constructions, and it consists in the combinations, constructions, and arrangements herein described and claimed.

An object of my invention is to provide a fuse construction particularly designed for the protection of delicate laboratory instruments and meters, radio hook-ups, and other electrical systems which employ electrical currents of high electromotive force and low amperage.

Another object is to provide a fuse construction having a fuse element consisting of the combination of one or more resistance wires and substances having comparatively low temperature fusing, melting, or ignition points.

Another object of my invention is to provide a fuse element consisting of the combination of one or more materials, one of the materials having a relatively high temperature melting point, and another of the materials having a relatively low melting ignition point, the material having the high temperature melting point being heated electrically for melting or igniting the material having the low melting or ignition point.

A further object is to provide a construction of the class described in which the fuse element includes one or more high resistance wires associated with an alloy? or substance having a low melting point, the high resistance wires being connected in series with the alloy or substance having a low melting or ignition point.

A further object of my invention is to provide a fuse construction having a fuse element, the resistance of which is reduced by coating a portion of the fuse element with a metal deposit.

A further object of my invention is to provide a fuse element having a resistance wire of variable cross sectional area, the portions of the wire having a reduced cross sectional area carrying a substance which will melt or explode at a comparatively low temperature, thereby breaking the wire.

A further object of my invention is to provide a fuse element which consists in part of a coiled resistance wire having deposited thereon small amounts of magnesium, phosphorous sesquisulphide, fulminate of mercury, or other substances, the explosion of which will blow the fuse.

Other objects and advantages will appear in the following specification, and the novel features of the invention will be particularly pointed out in the appended claims.

My invention is illustrated in the accompanying drawing, forming part of this application, in which Figure l is a perspective view of a fuse construction embodying my invention.

Figure 2 is a sectional view of the elements shown in Figure 1,

Figure 3 is a section taken along the line 3-3 of Figure 2, and

Figure 4 is a section taken along the line 4-4 of Figure 2.

In carrying out my invention, I provide a tubular casing 1 having terminal contact end cap members 2 and 2 which may be provided with central openings 3 and 3. These end cap members may be soldered or otherwise connected in series with an elongated fuse element 4.

The fuse element 4 may consist of aplurality or" resistance wires or filaments 5, 6, and 7, each of which may be joined together as is indicated at 8 with small amounts of substances consisting in whole or in part of material having a low melting or ignition point. These materials may. if desired, be applied in the form of paste. A portion of each of the resistance wires 5, 6, and 7 may be metal plated, as is indicated at 10. An unplated portion of these wires may be coiled, as

is indicated at 11. Each of these coiled portions may be provided with a deposit 9 consisting of similar substances having a low melting or flashing point.

It will of course be understood that the unplated portions of the wires may be filaments of extremely small cross-sectional area. Each of these may be supported by perforated partition walls 12, the perimeters of which may conform to the shape of the inner wall of the tube 1'.

The walls 12 may be held securely inposition by means of tubular sections 13 of sufficient size to frictionally engage the inner wall of the tube 1. The tubular sections 13, if desired, may be glued or cemented to this inner wall.

While the partition wall construction made of any suitable material, the preferred construction comprises one or more mica discs 14 which are reinforced on either side by metal discs 14'. The mica discs and the metal discs are provided with central openings 25 and 25',

respectively, through which the fuse element is threaded. These discs may be secured in their desired relationship to each other by the tubular sections 13.

The interior of the tube may also be provided with screen members 17 adapted to fit the interior walls of the tube 1 and having a central opening 17' through which the fuse element may be threaded. The screens may be positioned near each end of the tube and they serve to pre- 12 may be f vent any appreciable portion of the fuse element from being forcibly expelled through the openings 3 of the end caps 2.

While the substances indicated at 8 and 9 may be affixed to the wires in any suitable manner, I prefer to apply them to the wires in the form of a past which dries rapidly. The paste may consist of any adhesive substance intermixed with material having a low melting point, such as, for instance, magnesium, phosphorous sesquisulphide, or the like. These substances may be intermixed with the adhesive in a powdered form and they may be used either separately or in combination with each other. The flash point of the paste containing the magnesium powders ranges from 500 to 600 centigrade.

When the paste is mixed with the phosphorous sesquisulphide, the temperature at which the sulphide ignites is approximately 250 centigrade. The fulminate of mercury composition varies according to the method by which it is prepared, but its flash point may be stated as approximating 150 centigrade.

The ordinary resistance wire is not heated sufficiently to melt until it is heated to above 1400 centigrade. It is therefore apparent that by the application ofone or more of these substances, a fuse may be prepared which will blow at a much lower temperature than will a fuse having the ordinary resistance wire. It is also apparent that the flash point temperature of the fuse may be varied within wide limits.

These resistance wires may by reason of their reinforcement with a metal plating and their being supported by the partition walls 12, be safely made so small in cross-sectional area that as little as 1% of one ampere will raise the temmature of the wire to 1600 centigrade.

While the discs 14' may be made of any suitable metal, I have found that steel discs are particularly suitable for the purposes intended. The steel discs have the dual advantage of being rigid and having a relatively high melting point in combination with the mica disc 14 provide almost entirely a dead air compartment 15. When any portion of the fuse element is flashed or ignited, the are formed must jump across the mica discs. This tends to quench the spark.

Due to the small openings 25 and 25', the major portion of the are generated within any one compartment is prevented from escaping therefrom and is rapidly quenched by reason of the increased pressure of the expanded heated air within the compartment.

1 claim:

1. A tubular construction of the class described including a tubular casing, metal end caps secured to said casing, a fuse element soldered to said end caps and electrically connected in series with the-end caps, said fuse element consisting of a plurality of resistance wires, and a binding substance rigidly secured to said wires, said binding substance being connected in series with said wires and having a flash point below that of the wires.

2. A fuse construction including a casing, end caps fixedly connected to the casing, said casing being provided with a centrally disposed passage, a fuse element in said passage connected in series with said end caps, and a paste deposited on the fuse element, said paste comprising a binder and a substance intermixed therewith having a low flash point.

3. A fuse construction including a casing, end caps fixedly connected to the casing and being provided with a centrally disposed passage, a fuse element in said passage connected in series with said end caps, and a paste deposited on the fuse element, said paste comprising a binder and a substance intermixed therewith having a low flash point, said substance being a magnesium powder.

4. A fuse construction including a casing, end caps fixedly connected to the casing and being provided with a centrally disposed passage, a fuse element in said passage connected in serieswith said end caps, and a paste deposited on the fuse element, said paste comprising a binder and phosphorous sesquisulphide.

5. A fuse construction including a casing, end caps fixedly connected to the casing, a fuse element connected in series with said end caps, and a paste deposited on the fuse element, said paste consisting of a binder and a substance intermixed therewith having a low flash point, said fuse ele ment comprising a plurality of wires connected in series by said paste, one of said wires being coiled, a portion of said coiled wire carrying a deposit of magnesium.

6. A fuse construction including a casing, end caps fixedly connected to the casing, a fuse element connected in series with said end caps, and

a paste deposited on the fuse element, said paste consisting of a binder and a substance intermixed therewith having a low flash point, said fuse element consisting of a plurality of resistance wires connected in series by said paste, said fuse element being supported by a plurality of spacedapart partitions.

'7. A fuse construction including a casing, end caps fixedly connected to the casing, a fuse element connected in series with said end caps, and a paste deposited on the fuse element, said paste consisting of a binder and a substance intermixed therewith having a low flash point, said fuse element consisting of a plurality of resistance wires connected in series by said paste, said fuse element being supported by a plurality of spaced-apart partitions, one of said partitions consisting of a centrally disposed mica disc and metal discs positioned on either side of the mica disc.

EDWARD V. SUNDT. 

